Sheet processing apparatus

ABSTRACT

The present invention provides a sheet processing apparatus comprising a sheet holding device capable of storing supplied sheets, a first sheet stacking tray on which sheets are stacked at a downstream side of the sheet holding device in a sheet conveying direction and on which the sheets are subjected to processing, a sheet discharging device for discharging the sheets stacked on the first sheet stacking tray, a second sheet stacking tray on which the sheets discharged by the sheet discharging device are stacked, and a controller for controlling the sheet discharging device and the sheet holding device if sheet jam occurs at an upstream side of the sheet holding device, in such a manner that, after the sheets on the first sheet stacking tray are discharged onto the second sheet stacking tray, the sheets stored in the sheet holding device are discharged onto the first sheet stacking tray.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a sheet processing apparatusprovided in a main body of an image forming apparatus such as a copier,a printer or the like and adapted to process a sheet sent from the mainbody of the image forming apparatus, and, more particularly, it relatesto a sheet processing apparatus which can store sent sheets while thesheet is processed.

[0003] 2. Related Background Art

[0004] In recent years, as an option for an image forming apparatus suchas an electrophotographic copier, a laser beam printer or the like, asheet processing apparatus such as a sorter for sorting imaged sheetshas been developed. Such a sheet processing apparatus performs at leastone of sorting processing, stapling processing and aligning processingoperations with respect to the sheet.

[0005] In a sheet processing apparatus having a stapler for performingthe stapling processing, after sheets conveyed into a main body of thesheet processing apparatus are stacked on a processing tray through aconveying path provided within the main body, the stapling operation isperformed.

[0006] In the sheet processing apparatus for stapling a sheet stack (ora bundle of sheets), the sheets are stacked on the processing tray as asheet stack and the sheet stack is stapled at one position or pluralpositions (normally, two positions) while shifting the stapler asstapling means. While the stapling operation is being performed, sheetsfor a next job cannot be stacked on the processing tray. Thus, asheet-to-sheet distance between the successive jobs for the staplingoperation must be lengthened.

[0007] However, if the sheet-to-sheet distance is lengthened,productivity will be worsened. That is to say, the number of sheets tobe processed per unit time will be reduced. In order to prevent thereduction in the productivity, there has been proposed a sheetprocessing apparatus in which a sheet holding portion (buffer portion)for storing sheets is provided in a conveying path for conveying thesheet to a processing tray.

[0008] In such a sheet processing apparatus, while plural sheets stackedon the processing tray are being processed, plural succeeding sheets arestored in the sheet holding portion, and, when the processing isfinished, the sheets stored in the sheet holding portion are stacked onthe processing tray and the succeeding sheets are supplied onto theprocessing tray until a desired number of sheets are stacked.

[0009] There are two kinds of sheet processing apparatuses having such asheet holding portion. As a first kind, there is a sheet processingapparatus of sole stack discharging type in which, when the processingof the sheet stack on the processing tray is finished, the sheet stackon the processing tray is discharged and then the sheets stored in thesheet holding portion are discharged onto the processing tray (forexample, refer to Japanese Patent Application Laid-open No. 9-48545(FIGS. 1 and 2)). As a second kind, the Applicant proposed a sheetprocessing apparatus of simultaneous stack discharging type in which,when the processing of the sheet stack on the processing tray isfinished, an operation for discharging the sheet stack on the processingtray from the processing tray and an operation for discharging thesheets stored in the sheet holding portion onto the processing tray areperformed simultaneously. However, this sheet processing apparatus ofsimultaneous stack discharging type was not laid-opened on the prioritydate of this application and was laid-opened later (as Japanese PatentApplication Laid-open No. 2003-81517).

[0010] However, the two kinds of conventional sheet processingapparatuses had the following problems.

[0011] In both the sheet processing apparatus of sole stack dischargingtype and the sheet processing apparatus of simultaneous stackdischarging type, if a sheet is jammed at an upstream side of the sheetholding portion while the sheets are being stored in the sheet holdingportion, since the entire apparatus is stopped, the sheet stack stackedon the processing tray and the sheets held in the sheet holding portionremain within the apparatus, and, thus, a jam recovering time is greatlyincreased, thereby worsening processing efficiency.

[0012] Further, in the sheet processing apparatus of simultaneous stackprocessing type as the second kind, in a case where the sheet stack isstacked on the processing tray and the sheets are being stored in thesheet holding portion, for example, if adjustment such as coloradjustment is performed before a predetermined number of sheets are sentto the sheet holding portion, a succeeding sheet may be sent in adelayed manner. In such a case, while the succeeding sheet is being sentin the delayed manner, the processing of the sheet stack on theprocessing tray may be already finished.

[0013] However, in the sheet processing apparatus of this type, afterthe number of sheets sent during the processing of the sheet stack onthe processing tray are held in the holding portion, since thesimultaneous stack discharging operation in which the stored sheets aredischarged onto the processing tray and, at the same time, the sheetsstacked on the processing tray are discharged is performed, so long asthe predetermined number of sheets are not sent to the holding portion,even if the processing of the sheet stack on the processing tray isfinished, the sheet stack cannot be discharged outside. Thus, the sheetprocessing apparatus of simultaneous stack discharging type has poorprocessing efficiency.

SUMMARY OF THE INVENTION

[0014] An object of the present invention is to provide a sheetprocessing apparatus which enhances sheet processing efficiency.

[0015] Another object of the present invention is to provide an imageforming apparatus which include a sheet processing apparatus having highsheet processing efficiency to enhance image processing efficiency.

[0016] A further object of the present invention is to provide a sheetprocessing apparatus comprising a sheet holding device capable ofstoring supplied sheets, a first sheet stacking tray on which sheets arestacked at a downstream side of the sheet holding device in a sheetconveying direction and on which the sheets are subjected to processing,a sheet discharging device for discharging the sheets stacked on thefirst sheet stacking tray, a second sheet stacking tray on which thesheets discharged by the sheet discharging device are stacked, and acontroller for controlling the sheet discharging device and the sheetholding device when a succeeding sheet is not supplied to the sheetholding device for a predetermined time, in such a manner that, afterthe sheets on the first sheet stacking tray are discharged onto thesecond sheet stacking tray, the sheets stored in the sheet holdingdevice are discharged onto the first sheet stacking tray.

[0017] A still further object of the present invention is to provide asheet processing apparatus comprising a sheet holding device capable ofstoring supplied sheets, a first sheet stacking tray on which sheetsstored by the sheet holding device or sheets passed without stopping atthe sheet holding device are stacked and on which the sheets aresubjected to processing, a second sheet stacking tray on which thesheets discharged from the first sheet stacking tray are stacked, asheet conveying device for conveying the sheets stored in the sheetholding device and the sheets stacked on the first sheet stacking traytogether and for stacking the sheets stored in the sheet holding deviceonto the first sheet stacking tray after the sheet stacked on the firstsheet stacking tray are discharged onto the second sheet stacking tray,and a controller for controlling the sheet conveying device when asucceeding sheet is not supplied to the sheet holding device for apredetermined time, in such a manner that the sheets stacked on thefirst sheet stacking tray are discharged onto the second sheet stackingtray and the sheets stored in the sheet holding device are stacked ontothe first sheet stacking tray.

[0018] A further object of the present invention is to provide a sheetprocessing apparatus comprising a sheet holding device capable ofstoring supplied sheets, a first sheet stacking tray on which sheetsstored by the sheet holding device or sheets passed without stopping atthe sheet holding device are stacked and on which the sheets aresubjected to processing, a first sheet conveying device capable ofconveying the sheets stacked on the first sheet stacking tray by apredetermined amount at a downstream side of the sheets stored in thesheet holding device, a second sheet stacking tray on which the sheetsdischarged from the first sheet stacking tray are stacked, a secondsheet conveying device for conveying the sheets stacked on the firstsheet stacking tray and the sheets stored in the sheet holding devicetogether after the sheets stacked on the first sheet stacking tray areconveyed by the first sheet conveying device by the predetermined amountat the downstream side and for discharging the sheets stacked on thefirst sheet stacking tray onto the second sheet stacking tray and forstacking the sheets stored in the sheet holding device onto the firstsheet stacking tray, and a controller for controlling the sheet holdingdevice and the second sheet conveying device when a succeeding sheet isnot supplied to the sheet holding device for a predetermined time, insuch a manner that the sheets stacked on the first sheet stacking trayare discharged onto the second sheet stacking tray and the sheets storedin the sheet holding device are stacked onto the first sheet stackingtray.

[0019] A still further object of the present invention is to provide asheet processing apparatus comprising a sheet holding device capable ofstoring supplied sheets, a first sheet stacking tray on which sheets arestacked at a downstream side of the sheet holding device in a sheetconveying direction and on which the sheets are subjected to processing,a sheet discharging device for discharging the sheets stacked on thefirst sheet stacking tray, a second sheet stacking tray on which thesheets discharged by the sheet discharging device are stacked, and acontroller for controlling the sheet discharging device and the sheetholding device if sheet jam occurs at an upstream side of the sheetholding device, in such a manner that, after the sheets on the firstsheet stacking tray are discharged onto the second sheet stacking tray,the sheets stored in the sheet holding device are discharged onto thefirst sheet stacking tray.

[0020] A further object of the present invention is to provide a sheetprocessing apparatus comprising a sheet holding device capable ofstoring supplied sheets, a first sheet stacking tray on which sheetsstored by the sheet holding device or sheets passed without stopping atthe sheet holding device are stacked and on which the sheets aresubjected to processing, a second sheet stacking tray on which thesheets discharged from the first sheet stacking tray are stacked, asheet conveying device for conveying the sheets stored in the sheetholding device and the sheets stacked on the first sheet stacking traytogether and for stacking the sheets stored in the sheet holding deviceonto the first sheet stacking tray after the sheet stacked on the firstsheet stacking tray are discharged onto the second sheet stacking tray,and a controller for controlling the sheet conveying device if sheet jamoccurs at an upstream side of the sheet holding device, in such a mannerthat the sheets stacked on the first sheet stacking tray are dischargedonto the second sheet stacking tray and the sheets stored in the sheetholding device are stacked onto the first sheet stacking tray.

[0021] The other object of the present invention is to provide a sheetprocessing apparatus comprising a sheet holding device capable ofstoring supplied sheets, a first sheet stacking tray on which sheetsstored by the sheet holding device or sheets passed without stopping atthe sheet holding device are stacked and on which the sheets aresubjected to processing, a first sheet conveying device capable ofconveying the sheets stacked on the first sheet stacking tray by apredetermined amount at a downstream side of the sheets stored in thesheet holding device, a second sheet stacking tray on which the sheetsdischarged from the first sheet stacking tray are stacked, a secondsheet conveying device for conveying the sheets stacked on the firstsheet stacking tray and the sheets stored in the sheet holding devicetogether after the sheets stacked on the first sheet stacking tray areconveyed by the first sheet conveying device by the predetermined amountat the downstream side and for discharging the sheets stacked on thefirst sheet stacking tray onto the second sheet stacking tray and forstacking the sheets stored in the sheet holding device onto the firstsheet stacking tray, and a controller for controlling the sheet holdingdevice and the second sheet conveying device if sheet jam occurs at anupstream side of the sheet holding device, in such a manner that thesheets stacked on the first sheet stacking tray are discharged onto thesecond sheet stacking tray and the sheets stored in the sheet holdingdevice are stacked onto the first sheet stacking tray.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a schematic front sectional view of a copier as an imageforming apparatus of which a main body is provided with a sheetprocessing apparatus according to an embodiment of the presentinvention;

[0023]FIG. 2 is a control block diagram of the copier of FIG. 1;

[0024]FIG. 3 is a schematic front sectional view of the sheet processingapparatus according to the embodiment of the present invention;

[0025]FIG. 4 is a schematic front sectional view showing various drivingsystems of the sheet processing apparatus according to the embodiment ofthe present invention;

[0026]FIG. 5 is an enlarged view showing main parts of the sheetprocessing apparatus according to the embodiment of the presentinvention;

[0027]FIG. 6 is a view showing a condition that trailing end assist ofFIG. 5 is shifted;

[0028]FIG. 7 is a view showing a condition that the trailing end assistis further shifted from the condition of FIG. 6;

[0029]FIG. 8 is a control block diagram of the sheet processingapparatus of FIG. 3;

[0030]FIG. 9 is a flow chart for explaining an operation for discharginga sheet stack in the sheet processing apparatus of FIG. 3;

[0031]FIG. 10 is a view for explaining an operating timing between thetrailing end assist and a rocking roller pair;

[0032]FIG. 11 is a view for explaining an operating timing between thetrailing end assist and a rocking roller pair;

[0033]FIG. 12 is a view for explaining an operating timing between thetrailing end assist and a rocking roller pair and a first sheetdischarging roller pair;

[0034]FIGS. 13A and 13B are views for explaining an operation of thesheet processing apparatus in a case where sheets are not required to bestored during sheet processing, where FIG. 13A shows a condition that afirst sheet is sent into the sheet processing apparatus and FIG. 13Bshows a condition that the first sheet is received;

[0035]FIGS. 14A and 14B are views for explaining an operation of thesheet processing apparatus following the operations of FIGS. 13A and 13Bin the case where the sheets are not required to be stored during thesheet processing, where FIG. 14A shows a condition that the first sheetis passed through the first sheet discharging roller pair and FIG. 14Bshows a condition that the first sheet is dropped while straddlingbetween a stack tray and a processing tray;

[0036]FIGS. 15A and 15B are views for explaining an operation of thesheet processing apparatus following the operations of FIGS. 14A and 14Bin the case where the sheets are not required to be stored during thesheet processing, where FIG. 15A shows a condition that the first sheetis sent to the processing tray and FIG. 15B shows a condition that thefirst sheet is further sent to the processing tray;

[0037]FIGS. 16A and 16B are views for explaining an operation of thesheet processing apparatus following the operations of FIGS. 15A and 15Bin the case where the sheets are not required to be stored during thesheet processing, where FIG. 16A shows a condition that a second sheetis sent into the sheet processing apparatus and FIG. 16B shows acondition that the first sheet abuts against a stopper;

[0038]FIG. 17 is a view for explaining an operation of the sheetprocessing apparatus in the case where the sheets are not required to bestored during the sheet processing, in a condition that a third sheet isstacked on the processing tray;

[0039]FIGS. 18A and 18B are views for explaining an operation of thesheet processing apparatus following the operation of FIG. 17 in thecase where the sheets are not required to be stored during the sheetprocessing, where FIG. 18A shows a condition that a sheet stack startsto be discharged from the processing tray to the stack tray and FIG. 18Bshows a condition that the sheet stack is being discharged from theprocessing tray to the stack tray;

[0040]FIG. 19 is a view for explaining an operation of the sheetprocessing apparatus in the case where the sheets are not required to bestored during the sheet processing, in a condition that the sheet stackwas discharged from the processing tray onto the stack tray;

[0041]FIGS. 20A and 20B are views for explaining an operation of thesheet processing apparatus in a case where sheets are to be storedduring sheet processing, where FIG. 20A shows a condition that a firstsheet is sent into the sheet processing apparatus and FIG. 20B shows acondition that the first sheet is received up to a switchback point;

[0042]FIGS. 21A and 21B are views for explaining an operation of thesheet processing apparatus following the operations of FIGS. 20A and 20Bin the case where the sheets are to be stored during the sheetprocessing, where FIG. 21A shows a condition that the first sheet isreceived by a trailing end receiving portion and FIG. 21B shows acondition that the first sheet is pressed down against a lower conveyingguide plate by a trailing end pressing member;

[0043]FIGS. 22A and 22B are views for explaining an operation of thesheet processing apparatus following the operations of FIGS. 21A and 21Bin the case where the sheets are to be stored during the sheetprocessing, where FIG. 22A shows a condition that a second sheet is sentinto the sheet processing apparatus and FIG. 22B shows a condition thatthe second sheet is further sent;

[0044]FIGS. 23A and 23B are views for explaining an operation of thesheet processing apparatus following the operations of FIGS. 22A and 22Bin the case where the sheets are to be stored during the sheetprocessing, where FIG. 23A shows a condition that the second sheet isreceived up to the switchback point and FIG. 23B shows a condition thatthe second sheet is received by the trailing end receiving portion;

[0045]FIG. 24 is a view for explaining an operation of the sheetprocessing apparatus in the case where the sheets are to be storedduring the sheet processing, in a condition that the first and secondsheets are pressed down against the lower conveying guide plate by thetrailing end pressing member in an overlapped fashion;

[0046]FIGS. 25A and 25B are views for explaining an operation of thesheet processing apparatus following the operation of FIG. 24 in thecase where the sheets are to be stored during the sheet processing,where FIG. 25A shows a condition that a third sheet is sent in and FIG.25B shows a condition that the third sheet is sent in;

[0047]FIGS. 26A and 26B are views for explaining an operation of thesheet processing apparatus following the operations of FIGS. 25A and 25Bin the case where the sheets are to be stored during the sheetprocessing, where FIG. 26A shows a condition that a sheet stack startsto be discharged from a processing tray to a stack tray and FIG. 26Bshows a condition that the sheet stack and a buffer sheet are beingconveyed toward a discharging direction;

[0048]FIGS. 27A and 27B are views for explaining an operation of thesheet processing apparatus following the operations of FIGS. 26A and 26Bin the case where the sheets are to be stored during the sheetprocessing, where FIG. 27A shows a condition that the sheet stack isdischarged from the processing tray onto the stack tray and FIG. 27Bshows a condition that the buffer sheet is being sent to the processingtray;

[0049]FIGS. 28A and 28B are views for explaining an operation of thesheet processing apparatus following the operations of FIGS. 27A and 27Bin the case where the sheets are to be stored during the sheetprocessing, where FIG. 28A shows a condition that the buffer sheet isbeing sent to the processing tray and FIG. 28B shows a condition thatthe buffer sheet is being further sent to the processing tray;

[0050]FIG. 29 is a view for explaining an operation in a case where aprotruded length of a downstream end of the sheet stack is short from adownstream end of the buffer sheet;

[0051]FIG. 30 is a view for explaining a problem caused in a case wherethe sheet stack is discharged only by a rocking roller;

[0052]FIG. 31 is a flow chart for explaining an operation if sheet jamoccurs at an upstream side of the sheet processing apparatus;

[0053]FIG. 32 is a view showing a condition that a receiving roller pairand an inlet roller pair are spaced apart from each other;

[0054]FIG. 33 is a flow chart showing sorting processing;

[0055]FIGS. 34A and 34B are flow charts for explaining an operation of afirst sheet within the apparatus;

[0056]FIGS. 35A and 35B are flow charts for explaining an operation of abuffer last sheet;

[0057]FIGS. 36A, 36B and 36C are flow charts following to FIG. 35;

[0058]FIGS. 37A and 37B are flow charts for explaining a bufferoperation;

[0059]FIGS. 38A and 38B are flow charts for explaining an intermediateoperation;

[0060]FIG. 39 is a flow chart for explaining a post-processingoperation;

[0061]FIG. 40 is a flow chart following to FIG. 39;

[0062]FIG. 41 is a view showing a sheet processing apparatus accordingto another embodiment of the present invention; and

[0063]FIG. 42 is a flow chart for explaining an operation if sheet jamoccurs at an upstream side in the sheet processing apparatus of FIG. 41.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0064] Now, a sheet processing apparatus according to an embodiment ofthe present invention, and a copier as an example of an image formingapparatus having such a sheet processing apparatus will be explainedwith reference to the accompanying drawings. Incidentally, the imageforming apparatus may be a facsimile, a printer or a composite devicethereof, as well as the copier, and, thus, the image forming apparatusin which the sheet processing apparatus is provided is not limited tothe copier.

[0065] Incidentally, it is intended that dimensions, numerical values,materials, configurations and relative positions of constructional partsdescribed in the embodiments are not limited to given ones so long asthese are not specially identified.

[0066] In the embodiments, an example that a sheet processing apparatusis an optional apparatus in which the sheet processing apparatus isdetachably mounted to a main body of an image forming apparatus as anindependent apparatus will be explained. However, it should be notedthat, although the sheet processing apparatus of the present inventioncan be applied to a sheet processing apparatus provided integrally withthe image forming apparatus, since such a sheet processing apparatus ofintegral type does not differ specially from the sheet processingapparatus which will be described below, explanation thereof will beomitted.

[0067]FIG. 1 is a schematic sectional view showing a condition that thesheet processing apparatus is mounted to a copier. Incidentally, moreconcretely, the sheet processing apparatus is a finisher, for example.

[0068] (Image Forming Apparatus)

[0069] A copier 100 is constituted by a main body 101 and a sheetprocessing apparatus 119. A document feeding apparatus 102 is disposedon the main body 101 of the apparatus. Documents D are rested on adocument resting portion 103 by an operator and are separated one by oneby a feeding portion 104 and the separated document is sent to aregistration roller pair 105. Then, the document D is temporarilystopped by the registration roller pair 105, so that a loop is formed inthe document to correct skew-feeding. Thereafter, the document D ispassed through an introduction path 6 to reach a reading position 107,where an image formed on a surface of the document is read. The documentD left the reading position is passed through a discharging path 108 andthen is discharged onto a discharging tray 109.

[0070] Further, in a case where both surfaces of the document are read,first of all, when the document D is passed through the reading position107, the image on one surface of the document is read as mentionedabove. Thereafter, the document D is passed through the discharging path108 and is switchback-conveyed by turn-back roller pair 110, so that thedocument is sent to the registration roller pair 105 in a condition thata front surface of the document is turned over to a rear surface.

[0071] Then, similar to the reading of the image on one surface of thedocument D, skew-feeding of the document is corrected by theregistration roller pair 105 and, then, the document is passed throughthe introduction path 106 to reach the reading position 107, where animage on the other surface of the document is read. Then, the document Dis passed through the discharging path 108 and then is discharged ontothe discharging tray 109.

[0072] On the other hand, the image on the document passing through thereading position 107 is illuminated by light from an illumination system111. Reflection light reflected from the document is directed onto anoptical element (CCD or other element) 113 by a mirror 112, where imagedata is obtained. On the basis of the image data, a laser beam isilluminated onto a photosensitive drum 114 as image forming means,thereby forming a latent image. Incidentally, although not shown, it maybe designed so that the reflection light may be directly illuminatedonto the photosensitive drum 114 by the mirror 112 to form the latentimage.

[0073] The latent image formed on the photosensitive drum 114 receivestoner supplied from a toner supplying device (not shown), therebyforming a toner image. Sheets as recording media such as papers orplastic films are stacked in a cassette 115. In response to a recordingsignal, the sheet is fed out from the cassette 115 and is sent betweenthe photosensitive drum 114 and a transferring device 116 at apredetermined timing by a registration roller pair 150. Then, the tonerimage on the photosensitive drum 114 is transferred onto the sheet bythe transferring device 116. The sheet to which the toner image wastransferred is sent to a fixing device 117, where the toner image isfixed onto the sheet by heat and pressure.

[0074] In a case where images are formed on both surfaces of therecording medium, the sheet having one surface to which the image wasfixed by the fixing device 117 is passed through a both-surface path 118provided at a downstream side of the fixing device 117 and then is sentbetween the photosensitive drum 114 and the transferring device 116again, where an toner image is also transferred onto a rear surface ofthe sheet. Then, the toner image is fixed onto the rear surface by thefixing device 117. Then, the sheet is discharged outside (toward thefinisher 119).

[0075]FIG. 2 is a control block diagram of the entire copier. The entirecopier 100 is controlled by a CPU circuit portion 200. The CPU circuitportion 200 includes therein a ROM 202 for storing sequence for variousparts, i.e. control sequence, and a RAM 203 in which various informationare temporarily stored as desired. A document feeding apparatuscontrolling portion 204 serves to control a document feeding operationof the document feeding apparatus 102. An image reader controllingportion 205 controls the illumination system 108 and the like thereby tocontrol the reading of the document. An image signal controlling portion206 serves to receive read information from the image reader controllingportion 205 or image information sent from an external computer 207 viaan external I/F 208 and to process the information and then to send aprocessing signal to a printer controlling portion 209. The printercontrolling portion 209 controls the photosensitive drum 114 and thelike on the image processing signal from the image signal controllingportion 206 so that the image can be formed on the sheet.

[0076] An operating portion 210 can input sheet size information andinformation regarding the processing of the sheet (for example, staplingprocessing) by the operator utilizing the copier and can displayinformation regarding operating conditions of the main body 101 of thecopier and the finisher 119 as a sheet post-processing apparatus. Afinisher controlling portion 211 serves to control an operation of thefinisher 119 as the sheet post-processing apparatus. A FAX controllingportion 212 serves to control the copier so that the copier can be usedas a facsimile and can be communicated with other facsimile by a signal.

[0077] (Sheet Processing Apparatus)

[0078]FIG. 3 is a sectional view of the sheet processing apparatus. FIG.4 is a sectional view showing various driving systems. FIG. 8 is acontrol block diagram of the sheet processing apparatus. FIG. 9 is aflow chart for explaining an operation of the sheet processingapparatus. FIGS. 10 to 12 are views showing a relationship between ashifting speed of a trailing end assist 134 and a sheet conveying speedof a rocking roller pair 127 along lapse of time. FIG. 10 shows solestack discharging sequence in which a sheet stack is fed out by means ofthe trailing end assist 134 and the rocking roller pair 127. FIG. 11 isa view showing stack discharging control in a case where a startingspeed of the trailing end assist 134 differs from that of the rockingroller pair 127. FIG. 12 shows simultaneously stack discharging sequencein which the sheet stack and buffer sheets stored in a buffer unit 140are conveyed simultaneously by means of the trailing end assist, rockingroller pair and first conveying roller pair.

[0079] The sheet processing apparatus 119 has a function for bookbinding the sheet stack and thus includes a stapler unit 132 forstapling a portion near an edge of the sheet stack, a stapler 138 forstapling a central portion of the sheet stack, and a folding unit 139for folding a stapled position portion of the sheet stack stapled by thestapler 138 to form a booklet.

[0080] The sheet processing apparatus 119 according to the illustratedembodiment includes a buffer unit 140 for storing (buffering) aplurality of sheets in a straight overlapped condition during anoperation of the stapler unit 132.

[0081] Since the buffer unit 140 can store the plural sheets in thestraight overlapped condition, unlike to a conventional mechanism havinga buffer roller, the buffer unit can be more flattened, with the resultthat the sheet processing apparatus can be made compact andlight-weighted. Further, since the sheets can be stored in the straightcondition, unlike to the buffer roller, the sheet is not curled tofacilitate the handling of the sheet, and, thus, a sheet processing timeof the sheet processing apparatus can be shortened accordingly.

[0082] The sheet processing apparatus 119 is controlled by the finishercontrolling portion 211 shown in FIG. 8. A CPU 221 of the finishercontrolling portion 211 includes a ROM 222 for storing a control order(sequence) of the sheet processing apparatus 119 operated on the basisof command or instruction from the CPU circuit portion 200 of the mainbody of the copier, and a RAM 223 or the like for storing, each time,information required to control the sheet processing apparatus 119.Further, the finisher controlling portion 211 is connected to a sheetsurface detecting sensor 224 operated on the basis of an operation of asheet surface detecting lever 133 which will be described later. The CPU221 serves to control lifting/lowering of the stack tray 128 on thebasis of a detection signal of the sheet surface detecting sensor 224.The finisher controlling portion 211 serves to control, on the basis ofthe above-mentioned sequence, operations of an inlet conveying motor M2for rotating the inlet roller pair 121, buffer roller 124 and firstsheet discharging roller pair, a stack discharging motor M3 for rotatingthe rocking roller pair 127 and a return roller 130, and a clutch CLunder stack for transmitting and non-transmitting a rotation of thestack discharging motor M3 with respect to a lower roller 127 b.

[0083] Incidentally, the CPU circuit portion 200 and the finishercontrolling portion 211 shown in FIG. 2 may be formed integrally witheach other.

[0084] The clutch CL under stack shown in FIG. 4 is provided to absorb aspeed difference, for the reason that, since the lower roller 127 b andthe return roller 130 (described later) are rotated by the common stackdischarging motor M3, when the sheet or the sheet stack is conveyed bythe lower roller 127 b and the return roller 130, if slip occurs or if asheet conveying speed difference occurs between these rollers, the sheetor the sheet stack may be wrinkled or damaged.

[0085] (Explanation of Operation for Stapling and Discharging SheetStack)

[0086] When the operator selects the sheet stapling processing via theoperating portion 210 (refer to FIG. 2) of the copier 100, the CPUcircuit portion 200 controls various parts of the main body of theapparatus to bring the copier to a copying operation condition and sendsa sheet stapling processing signal to the finisher controlling portion211.

[0087] Incidentally, an explanation made with reference to FIGS. 13A to19 relates to a case where the CPU circuit portion 200 judges that alength of the sheet is great (for example, A3 size) on the basis ofsheet size information inputted by the operator via the operatingportion 210 or a case where the CPU circuit portion judges that aspecial sheet such as a thick paper, a thin paper, a tab paper, a colorpaper or the like having a property different from that of a normalsheet is used on the basis of sheet kind information. That is to say,the explanation made with reference to FIGS. 13A to 19 relates to a casewhere, after the sheet stack is discharged onto the stack tray 128, anoperation for stacking buffer sheets (described later) onto theprocessing tray 129 is started. Incidentally, of course, regardless ofthe length of the sheet and/or special sheet or normal sheet, theoperation described below may be performed.

[0088] The finisher controlling portion 211 starts to rotate the inletconveying motor M2 and the stack discharging motor M3 on the basis ofthe sheet stapling processing signal. Further, the finisher controllingportion 211 drives a buffer roller separating plunger SL1 (refer to FIG.4) to separate the buffer roller 124 from a lower conveying guide plate123 b and further drives a plunger (not shown) to separate an upperlower 127 a of the rocking roller pair 127 from the lower roller 127 b.Incidentally, the starting and stopping of the inlet conveying motor M2and the stack discharging motor M3 may be controlled successively inaccordance with a movement of the sheet.

[0089] A first sheet sent from the discharging roller pair 120 of themain body 101 of the copier 100 (refer to FIG. 1) is conveyed to theinlet roller pair 121 by conveyance of a receiving roller pair 137 shownin FIGS. 3 and 4 and guidance of a flapper 122. The receiving rollerpair 137 is rotated by a common conveying motor M1 for rotating thedischarging roller pair 120.

[0090] As shown in FIG. 13A, the inlet roller pair 121 is rotated by theinlet conveying motor M2 (refer to FIG. 4) to convey the first sheet P1.The first sheet P1 is conveyed to the first sheet discharging rollerpair 126 while being guided by a guide comprised of an upper conveyingguide plate 123 a and the lower conveying guide plate 123 b.

[0091] As shown in FIG. 13B, the sheet P1 is further conveyed by therotation of the first sheet discharging roller pair 126 and, as shown inFIG. 14A, is discharged onto the stack tray 128. As shown in FIG. 14B,the sheet P1 is dropped while straddling between the stack tray 128 andthe processing tray 129. Thereafter, as shown in FIGS. 15A and 15B, theupper roller 127 a is lowered by the plunger (not shown) to pinch thesheet between the upper roller and the lower roller 127 b (step S101 inFIG. 9).

[0092] In this case, the upper roller 127 a has already been rotated ina direction shown by the arrow by means of the stack discharging motorM3 (refer to FIG. 4). Further, the return roller 130 capable of engagingand disengaging with respect to the processing tray 129 is also rotatedin a direction shown by the arrow by means of the stack dischargingmotor M3 (refer to FIG. 4). However, the lower roller 127 b is rotatedidly by the action (step S102) of the clutch CL under stack (refer toFIG. 4). The reason is that, after the first sheet is stacked on theprocessing tray 129, when a second sheet, a third sheet and so on arestacked, if the lower roller 127 b is rotated positively, the lowerroller 127 b also pushes the first sheet toward a stopper 131, so thatthe first sheet may be wrinkled.

[0093] When about 150 msec is elapsed (step S103) after the clutch CLunder stack is operated, as shown in FIG. 16A, the sheet is slidinglylowered onto the processing tray 129 inclined downwardly and rightwardlyin a direction shown by the arrow by the rotations of the rocking rollerpair 127 and the return roller 130. In this case, the trailing endassist 134 is positioned at a waiting (or retraction) position (refer toFIG. 5). Before the sheet P1 abuts against the stopper 131, the upperroller 127 a is separated from the sheet P1. The sheet P1 abuts againstthe stopper 131 by the action of the return roller 130. Thereafter,alignment of the sheet in a width-wise direction is performed by a pairof alignment plates 144 a and 144 b (refer to FIG. 5) (step S104).

[0094] Thereafter, similarly, succeeding sheets are stacked on theprocessing tray 129. As shown in FIG. 17, when a predetermined number ofsheets are stacked on the processing tray 129, the sheets forming ssheet stack are stapled by the stapler unit 132 shown in FIGS. 3 and 4.Incidentally, in place of the fact that the sheet stack is stapled bythe stapler unit 132, the sheet stack may be punched by a punching unit(not shown).

[0095] When the sheet stack is stapled, as shown in FIG. 18A, the stacktray is shifted to a position where it can be detected by the sheetsurface detecting lever 133 and is waiting (or retracted) at a positionwhere the stack tray can easily receive the sheet stack (step S105).

[0096] As shown in FIG. 18B, the upper roller 127 a is rotated in thedirection shown by the arrow while pinching the sheet stack P betweenthis roller and the lower roller 127 b, and the trailing end assist 134pushes a trailing end of the sheet stack P to discharge the sheet stackonto the stack tray 128 (FIGS. 6 and 7). As shown in FIGS. 5, 6 and 7,the trailing end assist 134 is provided on a belt 142 which can berotated reversibly by a trailing end assist motor M4.

[0097] In this case, as shown in FIGS. 10 and 11, when starting times(T1) and starting speeds (132 mm/sec) of the rocking roller pair 127 andof the trailing end assist 134 are same and a same time (T2) is reachesat a same acceleration finishing speed (500 mm/sec), the rocking rollerpair 127 and the trailing end assist 134 can discharge the sheet stackwithout applying a tensile force or a compression force to the sheetstack (step S106).

[0098] However, as shown in FIG. 11, there is a case where the startingspeed of the trailing end assist 134 becomes greater than the startingspeed (for example, 300 mm/sec) of the rocking roller pair 127 due tothe presence of belts 143 and 142 for transmitting a rotational force ofthe trailing end assist motor M4 to the trailing end assist 134. In sucha case, the trailing end assist 134 does not start to shift but isstopped till a time T3 in which the sheet conveying speed of the rockingroller pair 127 reaches 300 mm/sec, and, when the sheet conveying speedof the rocking roller pair 127 is reached, the trailing end assiststarts to shift. That is to say, the trailing end assist 134 is startedwhen ΔT=(T3−T1) is elapsed after the rocking roller pair 127 is started(step S107). Incidentally, if the starting speed of the rocking rollerpair 127 is greater than the starting speed of the trailing end assist134, conversely, the starting speed of the rocking roller pair 127 isdelayed by the time ΔT. If the starting speed of the trailing end assist134 is the same as the starting speed of the rocking roller pair 127, ΔTis zero.

[0099] As such, by providing the time difference ΔT upon starting, ifthere is the difference in the starting speed between the rocking rollerpair 127 and the trailing end assist 134, the sheet stack can bedischarged without applying the tensile force or the compression forceto the sheet stack. Further, the rocking roller pair 127 does not formrubbing traces on the sheet stack, with the result that quality of thesheet stack and quality of images on the sheet stack are notdeteriorated.

[0100] The sheet stack starts to be fed out toward the stack tray 128 bythe rocking roller pair 127, trailing end assist 134 and return roller130 (step S108). The trailing end assist 134 is returned to its originalposition (home position) (step S110; operation corresponding to HPdischarging control in FIG. 12) after it was shifted by about 15 mm(step S109). As shown in FIG. 19, the sheet stack is discharged onto thestack tray 128 by the rocking roller pair 127. Thereafter, at a timewhen the upper lower 127 a of the rocking roller pair 127 is separatedfrom the lower roller 127 b, a series of sheet stack dischargingoperations are finished (steps S111 and S112).

[0101] In FIG. 18B, when the sheet stack starts to be discharged, afirst sheet for a next sheet stack has fed into the inlet roller pair121.

[0102] In the sheet processing apparatus 119 according to theillustrated embodiment, since the trailing end assist 134 urges thetrailing end of the sheet stack to convey the sheet stack, the surfaceof the sheet stack is not damaged and the sheet stack can be conveyedpositively, unlike to the case where the sheet stack is discharged byurging the rotating rollers against the surfaces of the sheet stack.

[0103] (Explanation of Buffering Operation)

[0104] Although the above-mentioned operational explanation relates to,for example, the case where the conveying distance between the sheetsare long and the stapling processing of the sheet stack can be performedbefore the next sheet is fed in, the following operational explanationrelates to a buffering operation in which the conveying distance betweensheets are short and, when succeeding sheets are fed in while the sheetstack is being processed, the succeeding sheets are stored (buffered)during a stapling processing operation.

[0105] The sheet processing apparatus 119 performs a buffering operationon the basis of buffering operation command from the finishercontrolling portion 211 when the CPU circuit portion 200 of the mainbody 101 judges that a distance between sheets fed from the main body101 of the copier 100 is smaller than the sheet stapling processingtime. In this case, buffer roller 124 is lowered by the plunger SL1(refer to FIG. 4) to be contacted with the lower conveying guide plate123 b.

[0106] In FIGS. 20A and 20B, it is assumed that the sheet stack isstacked on the processing tray 129 by the aforementioned operation.Further, it is assumed that the stapling processing is performed by thestapler unit 132 (refer to FIGS. 3 and 4) with respect to the sheetstack.

[0107] As shown in FIG. 20A, while the stapling processing is beingperformed with respect to the sheet stack P stacked on the processingtray 129, when a first sheet P1 for a next sheet stack is fed in, thesheet P1 is sent to the buffer roller 124 by the inlet roller pair 121.The buffer roller 124 is rotated by the inlet conveying motor M2 (referto FIG. 4) to convey the sheet P1 toward a downstream direction. In thiscase, an upper first sheet discharging roller 126 a of the first sheetdischarging roller pair 126 is separated from a lower first sheetdischarging roller 126 b by a first sheet discharging roller separatingplunger SL2 (refer to FIG. 4). Incidentally, in FIG. 4, since the firstsheet discharging roller separating plunger SL2 is overlapped with thebuffer roller separating plunger SL1 in a viewing direction, the plungerSL2 is not shown in FIG. 4. Further, the upper roller 127 a of therocking roller pair 127 is also separated from the lower roller 127 b bythe plunger (not shown).

[0108] As shown in FIG. 20B, when a trailing end of the sheet P1 reachesa switchback point SP, as shown in FIG. 21A, the sheet P1 is returnedtoward an upstream direction by a reverse rotation of the buffer roller124. At substantially the same time, the trailing end pressing member135 is separated from the lower conveying guide plate 123 b to open thetrailing end receiving stop portion 136. The reaching to the switchbackpoint SP can be detected on the basis of elapse of a predetermined timeafter the inlet path sensor S1 disposed in the vicinity of a downstreamside of the inlet roller pair 121 shown in FIG. 4 is operated by aleading end (downstream end) of the sheet or by counting the number ofrevolutions of the buffer roller 124.

[0109] After the downstream end of the sheet is detected, as shown inFIG. 21A, an upstream end of the sheet P1 is received by the trailingend receiving stop portion 136. Thereafter, as shown in FIG. 21B, thetrailing end pressing member 135 is returned to its original position,so that the sheet P1 is pressed against the lower conveying guide plate123 b by a friction member 141 provided on the trailing end pressingmember 135.

[0110] Thereafter, as shown in FIG. 22A, a second sheet P2 is sent in.The second sheet P2 is conveyed by the inlet roller pair 121. In thiscase, the sheet P2 is passed over the trailing end pressing member 135.Thereafter, as shown in FIG. 22B, the sheet P2 is also conveyed by thebuffer roller 124.

[0111] In this case, the first sheet P1 is pressed against the lowerconveying guide plate 123 b together with the second sheet P2 by thebuffer roller 124, so that the first sheet tries to follow the secondsheet P2 to be shifted toward the downstream direction. However, sincethe first sheet P1 is pressed against the lower conveying guide plate123 b by the friction member 141 provided on the trailing end pressingmember 135, the first sheet cannot be shifted.

[0112] Similar to the first sheet P1, the second sheet P2 is alsoreturned toward the upstream direction as shown in FIGS. 23A, 23B and 24when a trailing end of the second sheet reaches the switchback point SP.Then, the second sheet P2 is pressed against the lower conveying guideplate 123 b by the friction member 141 of the trailing end pressingmember 135 in a condition that the second sheet is overlapped with thefirst sheet P1.

[0113] Thereafter, as shown in FIG. 25A, a third sheet P3 is fed, and,when a trailing end of the sheet P3 is passed through the inlet rollerpair 121, as shown in FIG. 25B, the upper first sheet discharging roller126 a and the lower first sheet discharging roller 126 b pinch the firstto third sheets therebetween. In this case, the third sheet P3 isslightly protruded toward the downstream direction more than the firstand second sheets P1 and P2. Further, at this time, since the staplingprocessing of the sheet stack on the processing tray 129 is finished, asshown in FIG. 26A, the trailing end assist 134 is shifted along theprocessing tray 129, thereby pushing the trailing end of the sheet stackupwardly. As a result, a downstream end Pa of the sheet stack P isprotruded toward the downstream direction more than a downstream end P3a of the third sheet P3 by a length of L.

[0114] Then, as shown in FIG. 26B, the upper roller 127 a is alsolowered to pinch the three sheets P1 to P3 and the sheet stack P betweenthe upper roller and the lower roller 127 b. In accordance with this,the trailing end pressing member 135 is separated from the second sheetP2 to release the first sheet P1 and the second sheet P2.

[0115] Thereafter, the three sheets P1 to P3 and the sheet stack P areconveyed by the rocking roller pair 127 while being pinched by therocking roller pair. As shown in FIGS. 27A and 27B, when the sheet stackP is discharged onto the stack tray 128, the trailing ends of the firstsheet P1 and the second sheet P2 leave the first sheet dischargingroller pair 126 and the upstream end of the third sheet is received bythe processing tray 129.

[0116] In FIG. 27B, as shown, in a case where the starting times (T1)and the starting speeds (132 mm/sec) of the first sheet dischargingroller pair 126, the rocking roller pair 127 and the trailing end assist134 are the same, when the same time (T2) is reached at the sameacceleration finishing speed (500 mm/sec), the first sheet dischargingroller pair 126, rocking roller pair 127 and trailing end assist 134 candischarge the sheet stack without applying the tensile force and thecompression force to the sheet stack and the three sheets. However, ifthere is a difference in the starting speed, as is in the step S107 inFIG. 9, by operating the first sheet discharging roller pair, rockingroller pair and trailing end assist with the time difference of ΔT, thesheet stack can be discharged without applying the tensile force and thecompression force to the sheet stack and the three sheets. Further, thefirst sheet discharging roller pair 126 and the rocking roller pair 127do not form rubbing traces on the sheet stack, with the result thatquality of the sheet stack and quality of images on the sheet stack arenot deteriorated.

[0117] As shown in FIGS. 28A and 28B, the three sheets are slidinglyconveyed on the processing tray 129 by the rocking roller pair 127 andthe return roller 130 and are received by the stopper 131. Meanwhile,the stack tray 128 is once lowered to lower the upper surface of thesheet stack below the sheet surface detecting lever 133 and then liftedagain and is stopped at a time when the sheet surface detecting lever133 is operated by the upper surface of the sheet stack. As a result,the upper surface of the sheet stack on the stack tray 128 can bemaintained at a predetermined height. Thereafter, the sheets aresuccessively stacked on the processing tray 129 without being stored onthe lower conveying guide plate 123 b. When a predetermined number ofsheets are stacked, these sheets are stapled. During such staplingoperation, first three sheets for a next sheet stack are stored on thelower conveying guide plate 123 b.

[0118] Incidentally, in the above-mentioned explanation, while anexample that the three sheets are stored on the lower conveying guideplate 123 b was explained, the number of sheets (buffer sheets) to bestored is not limited to three since such number is varied with thelength of the sheet, stapling time and sheet conveying speed.

[0119] As mentioned above, in the sheet processing apparatus 119according to the illustrated embodiment, as shown FIG. 26A, thedownstream end Pa of the sheet stack P is protruded in the downstreamdirection more than the downstream end P3 a of the third sheet P3 by thelength of L, for the following reason. Incidentally, downstream ends P1a and P2 a of the first and second sheets P1 and P2 are positioned atthe upstream side of the downstream end P3 a of the third sheet P3.

[0120] If the protruded length of the downstream end is L1 smaller thanthe length L, as shown in FIG. 29, the protruded length of thedownstream end also becomes L1. Thus, after the sheet stack P isdischarged onto the stack tray 128, a length or distance through whichthe three buffer sheets are grasped by the rocking roller pair 127becomes shorter, with the result that the rocking roller pair may failto grasp the three sheets and, thus, the three sheets may not be sent tothe processing tray 129 positively. Accordingly, in order that therocking roller pair 127 can grasp the buffer sheets positively and sendthem to the processing tray 129, the sheet stack is protruded by thelength L with respect to the buffer roller.

[0121] Further, if the protruded length is shorter, a contact areabetween the buffer sheet and the sheet stack becomes greater to contactthe sheet stack with the buffer sheet more closely, with the result thatthe sheet stack tends to be dropped onto the stack tray 128 more slowly.In such a case, when the buffer sheets are fed to the processing tray129 by the reverse rotation of the rocking roller pair 127, the sheetstack may enter into the rocking roller pair 127 while being closelycontacted with the. buffer sheet, thereby causing damage of the sheetstack or sheet jam. Accordingly, also in order to improve a separatingability between the sheet stack and the buffer sheet, the sheet stack isprotruded by the length L with respect to the buffer roller.

[0122] In addition, in the sheet processing apparatus 119 according tothe illustrated embodiment, the trailing end of the sheet stack ispushed by the trailing end assist 134. When the trailing end assist 134pushes the trailing end of the sheet stack to convey the sheet stack,unlike to the case where the sheet stack is discharged while urging therotating rollers against the surfaces of the sheet stack, the surfacesof the sheet stack are not damaged and the sheet stack can be conveyedpositively.

[0123] That is to say, as shown in FIG. 30, if the sheet stack isdischarged by the rocking roller pair 127 alone, due to a difference infriction between the upper roller 127 a and the lower roller 127 b withrespect to the sheet and a difference in a rotational speed betweenthese rollers, sheet conveying amounts attained by these rollers maydiffer from each other, with the result that deviation may occur betweenthe uppermost sheet and the lowermost sheet. In such a case, the rockingroller pair 127 may be slidingly rotated with respect to the sheet,thereby damaging the sheet. Further, the entire sheet stack may bedischarged while being twisted, with the result that the sheet stack maynot be discharged smoothly and the processing time may be increased.Further, if the entire sheet stack is twisted, any sheet or sheets maybe torn at the stapled area or areas, thereby spoiling the sheet stack.

[0124] Further, such a phenomenon is apt to occur in a case where thepinching force of the rocking roller pair 127 with respect to the sheetstack is increased to discharge the sheet stack more positively.Conversely, if the pinching force is decreased, the sheet stack cannotbe positively conveyed. Accordingly, it is difficult to set the pinchingforce of the rocking roller pair 127.

[0125] In consideration of the above circumstances, in the sheetprocessing apparatus according to the illustrated embodiment, since thesheet stack is discharged not only by the rocking roller pair 127 butalso by the trailing end assist 134, there are no sliding rotation withrespect to the sheet and no twist of the sheet stack as mentioned above,with the result that the sheet and the sheet stack are not damaged andthe sheet stack can be discharged smoothly and quickly. Further, thesheet stack can be discharged without managing the pinching force of therocking roller pair 127 strictly.

[0126] Next, an operation of the sheet processing apparatus 119 will beexplained in a case where sheet is jammed at an upstream side of thesheet processing apparatus 119 will be explained.

[0127] If sheet jam occurs (step S203 in a flow chart of FIG. 31) at anupstream side of the buffer unit 140, i.e., at an upstream side of theinlet roller pair 121 after the copying operation of the copier 100(FIG. 1) is started (step S201) and before the copying operation isfinished (step S202), the CPU circuit portion 200 (refer to FIGS. 2 and8) of the main body 101 of the copier sends a jam generating signal tothe CPU 221 of the finisher controlling portion 211 and stops therotations of the sheet conveying rollers within the main body 101.

[0128] Further, if the jam occurs in the receiving roller pair 137, theCPU 221 stops the rotation of the receiving roller pair 137 and sends ajam generating signal to the CPU circuit portion 200. The CPU circuitportion 200 which received the jam generating signal stops the rotationsof the sheet conveying rollers within the main body 101, therebypreventing the sheet from being sent in the sheet processing apparatus119.

[0129] Thereafter, the CPU 221 judges whether or not the hold sheet(buffer sheet) is stacked on the guide 123 (refer to FIG. 4) as thesheet holding portion, on the basis of the detecting operation of theinlet path sensor S1 (step S204). If the inlet path sensor S1 does notdetect the holding sheet, the CPU 221 judges that the hold sheet is notstored in the guide 123 and judges whether the sheet stack stacked onthe processing tray 129 can be discharged or not (step S205). If it isjudged that the number of sheets can be stapled, the program of the CPUis shifted to control for stapling the sheet stack by the stapler unit132 and for forcibly discharging the sheet stack solely (step S206). Onthe other hand, if it is judged that the number of sheets cannot bestapled (step S205), the sheet stack is left as it is on the processingtray 129.

[0130] The CPU 221 discharges the sheet stack onto the stack tray by theoperations shown in FIGS. 17A to 19 (step S207). Thereafter, the CPU 221stops the operation of the entire sheet processing apparatus 119 (stepS208).

[0131] In the step S204, when the sheet is detected by the inlet sensorS1, the CPU 221 judges that the hold sheets are stored on the guide 123and then judges whether the sheet stacked on the processing tray 129 canbe discharged or not (step S209). Since the fact that there is the holdsheet on the guide 123 means that a number of sheets which can bedischarged are stacked on the processing tray 129, the program of theCPU 221 is shifted to control for stapling the sheet stack by thestapler unit 132 and for forcibly discharging the sheet stack on theprocessing tray 129 and the hold sheet simultaneously (step S210).

[0132] The CPU 221 discharges the sheet stack onto the stack tray 128 bythe operations shown in FIGS. 25A to 28B and discharges the hold sheetsin the guide 123 onto the processing tray 129 (step S207). Thereafter,the CPU 221 stops the operation of the entire sheet processing apparatus119 (step S208).

[0133] The sheet jammed in the receiving roller pair 137 can easily beremoved by separating upper rollers of the receiving roller pair 137 andthe inlet roller pair 121 from lower rollers thereof to release theguide 123 as shown in FIG. 32. Further, even if the sheet is jammed at adownstream side of the receiving roller pair 137, the jammed sheet canbe removed by separating the upper first sheet discharging roller 126 aand the upper roller 127 a from the lower first sheet discharging roller127 b and the lower roller 127 b. The upper rollers of the receivingroller pair 137 and of the inlet roller pair 121 are provided on abracket 190 rotatable around a shaft 124 a of the buffer roller 124.

[0134] As such, in the sheet processing apparatus 119 according to theillustrated embodiment, if the sheet jam occurs at the upstream side ofthe sheet processing apparatus 119, since the sheets on the processingtray 129 are forcibly discharged onto the stack tray 128 and the sheetsheld in the buffer unit 140 are forcibly discharged onto the processingtray 129, the stapled sheet stack can be obtained by the operatorquickly regardless of occurrence of the sheet jam, thereby enhancing theprocessing efficiency and operator's operability.

[0135] Further, since the sheets held in the buffer unit 140 areforcibly discharged onto the processing tray 129, jam treatment can befacilitated, thereby enhancing a jam treating ability.

[0136] In addition, since the sheets held in the buffer unit 140 areforcibly discharged onto the processing tray 129, only sheets for jamrecovery can be held within the sheet processing apparatus, with theresult that a recovery starting sheet can easily be recognized.

[0137] Further, if the sheet stack is left on the processing tray 129 asit is for a long term without finding the sheet jam, for example, theexternally protruded portion shown in FIGS. 20A and 20B may be flexeddownwardly by its own weight, thereby deforming the sheet stack.However, in the sheet processing apparatus 119 according to theillustrated embodiment, if the jam occurs, since the sheet stack isforcibly discharged, deformation of the sheet stack can be prevented.

[0138] Next, an operation of the sheet processing apparatus will beexplained with reference to flow charts shown in FIGS. 33 to 40 in acase where the distance between succeeding sheets fed into the sheetprocessing apparatus 119 is increased in comparison with the previoussheet-to-sheet distance, for example, in a case where the sheetprocessing apparatus 119 is mounted to a main body of a color copier inwhich the sheet-to-sheet distance is increased as a result of colorimage quality adjustment. Incidentally, in the flow charts, a case wheretwo sheets are buffered will be explained.

[0139]FIG. 33 is a flow chart for explaining a schematic operation ofthe entire sheet processing apparatus 119 and is a flow chart forsorting processing. Operations of various parts shown in the flow chartare performed by the finisher controlling portion 211 shown in FIG. 8.

[0140] In the sorting processing (step S301), the sheet processingapparatus 119 performs one of operations among an inboard first sheetoperation (step S307), a buffer last sheet operation (step S308), abuffer sheet operation (step S309) and an intermediate sheet operation(step S310) on the basis of judgments whether the sheet to be stacked onthe processing tray 129 is a first sheet or not (step S302), whether avalue of a buffer counter is 1 or not (step S303) and whether a previoussheet is a last sheet for the sheet stack or not (step S304).

[0141] The inboard first sheet operation (step S307) in FIG. 33 is anactions performed from when the first sheet is stacked on the processingtray 129 to when the sheet processing is started, as shown by steps S401to S420 in FIGS. 34A and 34B.

[0142] The buffer last sheet operation (step S308) in FIG. 33 is actionsperformed from when the buffer sheet is stacked on the processing tray129 to when the post-processing operation is started, as shown by a stepS501 in FIG. 35A to a step S535 in FIG. 36C.

[0143] The buffer sheet operation (step S309) in FIG. 33 is actions forstoring (buffering) the buffer sheets on the guide 123, as shown bysteps S601 to S613 in FIGS. 37A and 37B.

[0144] The intermediate sheet operation (S310) in FIG. 33 is actionsperformed from when the second sheet and so on are stacked on theprocessing tray 129 to when the sheet processing is started, as shown bysteps S701 to S716 in FIGS. 38A and 38B.

[0145] A start post-processing in a step S419 of FIG. 34B, a step S534of FIG. 36C and a step S715 of FIG. 38B is an operation for performingthe post-operation after the sheet discharged from the main body 101 ofthe copier 100 is stacked on the processing tray 129, as shown by stepsS810 to S824 in FIG. 39.

[0146] First of all, the CPU 221 (refer to FIG. 8) controls a frontaligning motor M5 and a rear aligning motor M6 to approach, to thesheet, front and rear aligning plates 144 a and 144 b (refer to FIG. 5)which disposed on both sides along the sheet conveying direction andwhich can be moved toward and away in a direction transverse to thesheet conveying direction, thereby aligning front and rear edges of thesheet (steps S801 and S802). If a large size sheet such as a B4 sizesheet which must be aligned by two times is used (step S803), after 100msec is elapsed (step S804), the front aligning plate 144 a and the rearaligning plate 144 b are once separated from the sheet and are retracted(or waiting) (steps S805 and S806). Then, after 50 msec is elapsed (stepS807), the front aligning plate 144 a and the rear aligning plate 144 b(refer to FIG. 5) are approached to the sheet again to perform a secondaligning operation (step S808). After a series of aligning operationsare finished (step S809), the CPU 221 control the stack dischargingmotor M3 to stop the reverse rotation of the rocking roller pair 127(step S810).

[0147] Thereafter, the CPU 221 judges whether a fed sheet is the lastsheet of the sheet stack or not on the basis of last sheet informationregarding the sheet stack from the CPU circuit portion 200 of the mainbody 101 or the sheet number from the counter for counting the sheetnumber (step S811 in FIG. 40). If the sheet is not the last sheet, theCPU 221 controls the front aligning motor M5 and the rear aligning motorM6 (refer to FIG. 8) to return the front aligning plate 144 a and therear aligning plate 144 b (refer to FIG. 5) to the retraction (orwaiting) position (steps S822 and S823).

[0148] In a step S811, if the sheet is the last sheet, when the sheetstack is stapled by the stapler unit 132 (step S812), the CPU 221controls a stapler shift motor M8 to shift the stapler 166 to a staplingposition (position where the sheet stack is stapled) and controls astapler motor M9 to staple the sheet stack by means of the stapler 166(steps S813 and S814). Thereafter, the CPU 221 controls the trailing endassist motor M4 (refer to FIGS. 5 to 8) to protrude (pre-protrude) morethan the stored sheets by the length L by means of the trailing endassist 134 as shown in FIGS. 26A and 26B (steps S815 and S816).

[0149] Thereafter, when the CPU 221 judges that the stapled sheet stackcannot be discharged simultaneously (the sheet stack is not a sheetstack not subjected to simultaneous stack discharging) on the basis ofthe sheet property information such as a sheet size, a sheet material(paper quality), a thick sheet, a thin sheet, a tab sheet, a color sheetand the like or when the sheet next to the stapled sheet stack cannot bebuffered (step S817), the CPU controls the stack discharging motor M3 todischarge only the stapled sheet stack from the processing tray 129 ontothe stack tray 128 (sole stack discharging) and the post-processingoperation is completed (steps S822, S823 and S824).

[0150] Also, if the next sheet is jammed and is not sent to the bufferunit 140, the CPU 221 controls the stack discharging motor M3 todischarge only the stapled sheet stack from the processing tray 129 ontothe stack tray 128 (sole stack discharging) and the post-processingoperation is completed (steps S818, S821 and S824).

[0151] By doing so, in the sheet processing apparatus, since the stapledsheet stack can be discharged onto the stack tray 128 without storingthe sheet stack on the processing tray 129 unnecessarily for a longterm, the processing efficiency of the sheet processing apparatus 119can be enhanced, with the result that the sheet stack can be presentedby the operator quickly.

[0152] Further, since the stapled sheet stack is not left as it is onthe processing tray 129 for a long term, for example, the externallyprotruded portion shown in FIGS. 20A and 20B is not flexed downwardly byits own weight, thereby preventing the deformation of the sheet stack.

[0153] Even when the succeeding sheet can be sent to the buffer unit140, due to the slip of the feeding rollers within the main body 101 ofthe apparatus and/or image adjustment, if the succeeding sheet isdelayed so that the sheet stack on the processing tray 129 becomespossible to be discharged onto the stack stray 128 before the succeedingsheet reaches the buffer unit 140, for example, at the upstream side ofthe registration roller pair 150 shown in FIG. 1, the CPU 221 controlsthe stack discharging motor M3 to discharge only the stapled sheet stackfrom the processing tray 129 onto the stack tray 128 (sole stackdischarging) and the post-processing operation is completed (steps S819,S821 and S824).

[0154] By dosing so, in the sheet processing apparatus, since thestapled sheet stack can be discharged onto the stack tray 128 withoutstoring the sheet stack on the processing tray 129 unnecessarily for along term, the processing efficiency of the sheet processing apparatus119 can be enhanced, with the result that the sheet stack can bepresented by the operator quickly.

[0155] Further, since the stapled sheet stack is not left as it is onthe processing tray 129 for a long term, for example, the externallyprotruded portion shown in FIGS. 20A and 20B is not flexed downwardly byits own weight, thereby preventing the deformation of the sheet stack.

[0156] If both the sheets on the processing tray 129 and the sheetsstored on the guide 123 do not satisfy the condition in the steps S818and S819, the CPU 221 controls the inlet conveying motor M2, stackdischarging motor M3 and clutch CL under stack thereby to discharge thesheet stack on the processing tray 129 onto the stack tray 128 and atthe same time to discharge the stored sheets from the guide 123 onto theprocessing tray 129. That is to say, the simultaneous stack dischargingis performed (steps S820 and S824).

[0157] The sole stack discharging operation (step S821) in FIG. 40 isactions for discharging only the stapled sheet stack stacked on theprocessing tray 129 without discharging the stapled sheet stacksimultaneously with the buffer sheets, as shown in the steps S101 toS112 of FIG. 9.

[0158] While the above-mentioned sheet processing apparatus was a sheetprocessing apparatus of simultaneous stack discharging type, presentinvention can be applied to a sheet processing apparatus of sole stackdischarging type as shown in FIG. 41. Such a sheet processing apparatus10 is mounted to a main body 16 of an image forming apparatus (forexample, a copier) and is used as a copier 15.

[0159] In this sheet processing apparatus 10, sheets fed from the mainbody 16 of the apparatus by a sheet discharging roller pair 17 arepassed through a straight path 20 and are successively stacked onto aprocessing tray 11, and, when a predetermined number of sheets arestacked, stacked sheets are stapled by a stapler unit 19. Thereafter, byrotating upper and lower rollers 18 a and 18 b of a rocking roller pair18, these rollers discharge the sheet stack while pinching the sheetstack therebetween.

[0160] While the sheet stack is being stapled by the stapler unit 19,supplied sheets are guided by a conveying passage 12 and are stored(buffered) in a buffer roller path 14 formed around a buffer roller 13,and, when a stapling processing operation is finished, the stored sheetsare discharged onto the processing tray 11. The number of sheets to bestored (buffer sheets) is the sheet number corresponding to a timerequired for stapling the sheet stack. The buffer roller 13 and thebuffer roller path 14 constitute parts of a buffer unit 23.

[0161] Also in such a sheet processing apparatus 10, if a sheet isjammed at an upstream side of the buffer roller path 14, the stapledsheet stack is on the processing tray 11 is discharged by continuingonly the operation of the sheet processing apparatus 10 without stoppingthe operation of the entire sheet processing apparatus 10.

[0162] That is to say, in a flow chart shown in FIG. 42, from when thecopier 15 starts a copying operation (step S901) to when copyingoperation is finished (step S903), if sheet jam occurs at an upstreamside of the buffer unit 23, i.e., at an upstream side of the conveyingpassage 12 (step S902), a CPU circuit portion 24 in the main body 16 ofthe copier sends a jam generating signal to a CPU 21 of the finishercontrolling portion 20 and stops rotation of sheet conveying rollerswithin the main body 16.

[0163] Thereafter, the CPU 21 judges whether or not there is a holdsheet (buffer sheet) in the buffer roller path 14 by a detectingoperation of a buffer sensor S2 (step S904). If the hold sheet is notdetected by the buffer sensor S2, it is judged that there is no holdsheet in the buffer roller path 14, and, the CPU judges whether thesheets stacked on the processing tray 11 can be discharged or not (stepS905). If the sheets can be discharged, sheet stack is forciblydischarged solely (steps S906 and S907). If the sheets cannot bedischarged (step S905), the sheet stack remains on the processing trayin a stacked condition. Then, the CPU 21 stops the operation of theentire sheet processing apparatus 10 (step S918).

[0164] In the above-mentioned step S904, if the sheet is detected by thebuffer sensor S1, the CPU 21 judges that the hold sheet is held in thebuffer roller path 14, and, since the sheet stack which can bedischarged is stacked on the processing tray 11, the sheet stack isdischarged out of the apparatus (steps S909 and S910). Thereafter, theCPU 21 discharges the sheet stored in the buffer roller path 14 onto theprocessing tray 11 (steps S911 and S912). Lastly, the CPU 21 stops theoperation of the entire sheet processing apparatus 10 (step S913).

[0165] As such, in the sheet processing apparatus 10 according to theillustrated embodiment, if the sheet jam occurs at the upstream side ofthe sheet processing apparatus 10, since the sheets held in the bufferroller path 14 are forcibly discharged onto the processing tray 11 afterthe sheets on the processing tray 11 are forcibly discharged onto thestack tray 22, the operator can obtain the sheet stack quicklyregardless of occurrence of the sheet jam, with the result that theprocessing efficiency can be enhanced and operator's operability canalso be enhanced.

[0166] Further, since the sheets held in the buffer roller path 14 areforcibly discharged onto the processing tray 11, the jam treatment canbe facilitated, thereby enhancing the jam treating ability.

[0167] In addition, since the sheets held in the buffer roller path 14are forcibly discharged onto the processing tray 11, only sheets for jamrecovery can be held within the sheet processing apparatus, with theresult that a recovery starting sheet can easily be recognized.

[0168] Further, if the sheet stack is left on the processing tray 11 asit is for a long term without finding the sheet jam, for example, theexternally protruded portion may be flexed downwardly by its own weight,thereby deforming the sheet stack. However, in the sheet processingapparatus 10 according to the illustrated embodiment, if the jam occurs,since the sheet stack is forcibly discharged, deformation of the sheetstack can be prevented.

[0169] In the above-mentioned explanation, while an example that theposition of the sheet is detected by the sensor was explained, theposition of the sheet may be judged on the basis of sheet holdinginformation (memory information) managed within the CPU 221.

[0170] Further, in the sheet processing apparatus, although the sheetstack is stapled after width alignment for aligning the sheet stack onthe processing tray 129 from both sides and trailing end alignment areperformed, the sheet stack may be discharged onto the stack tray 128after the width alignment and the trailing end alignment withoutstapling the sheet stack.

[0171] As mentioned above, in the sheet processing apparatus, when thesucceeding sheet is not supplied to the buffer unit for thepredetermined time, since the control portion controls the rockingroller pair and the buffer unit, in such a manner that, after the sheetson the processing tray are discharged onto the stack tray, the sheetsheld in the buffer unit are discharged onto the processing tray, forexample, the operator can obtain the stapled sheet stack quicklyregardless of the occurrence of the sheet jam, thereby enhancing theprocessing efficiency and the operator's operability.

[0172] Further, since the sheets held in the buffer roller path areforcibly discharged onto the processing tray, the jam treatment can befacilitated, thereby enhancing the jam treating ability.

[0173] In addition, since the sheets held in the buffer roller path areforcibly discharged onto the processing tray, only sheets for jamrecovery can be held within the sheet processing apparatus, with theresult that a recovery starting sheet can easily be recognized.

[0174] Further, if the sheet stack is left on the processing tray as itis for a long term without finding the sheet jam, the externallyprotruded portion may be flexed downwardly by its own weight, therebydeforming the sheet stack. However, in the sheet processing apparatus,if the jam occurs, since the sheet stack is forcibly discharged, thedeformation of the sheet stack can be prevented.

[0175] In the sheet processing apparatus, when the succeeding sheet isnot supplied to the buffer unit for the predetermined time, since thefinisher controlling portion controls the rocking roller pair, in such amanner that the sheets stacked on the processing tray are dischargedonto the stack tray and the sheets held in the buffer unit aredischarged onto the processing tray, the operator can obtain the stapledsheet stack quickly regardless of the occurrence of the sheet jam,thereby enhancing the processing efficiency and the operator'soperability.

[0176] Further, since the sheets held in the buffer unit are forciblydischarged onto the processing tray, the jam treatment can befacilitated, thereby enhancing the jam treating ability.

[0177] In addition, since the sheets held in the buffer unit areforcibly discharged onto the processing tray, only sheets for jamrecovery can be held within the sheet processing apparatus, with theresult that a recovery starting sheet can easily be recognized.

[0178] Further, if the sheet stack is left on the processing tray as itis for a long term without finding the sheet jam, for example, theexternally protruded portion shown in FIGS. 20A and 20B may be flexeddownwardly by its own weight, thereby deforming the sheet stack.However, in the sheet processing apparatus, if the jam occurs, since thesheet stack is forcibly discharged, deformation of the sheet stack canbe prevented.

[0179] In the sheet processing apparatus, when the succeeding sheet isnot supplied to the buffer unit for the predetermined time, since thefinisher controlling portion controls the buffer unit and the rockingroller pair, in such a manner that the sheets stacked on the processingtray are discharged onto the stack tray and the sheets stored in thebuffer unit are stacked onto the processing tray, since the stapledsheet stack can be discharged onto the stack tray without storing thesheet stack on the processing tray unnecessarily for a long term, theprocessing efficiency of the sheet processing apparatus can be enhanced,with the result that the sheet stack can be presented by the operatorquickly.

[0180] Further, since the stapled sheet stack is not left as it is onthe processing tray for a long term, for example, the externallyprotruded portion shown in FIGS. 20A and 20B is not flexed downwardly byits own weight, thereby preventing the deformation of the sheet stack.

[0181] Further, after the trailing end assist conveys the sheets stackedon the processing tray toward the stack tray by the predeterminedamount, since the rocking roller pair conveys the sheet held in thebuffer unit and the sheet stacked on the processing tray simultaneouslyto discharge the sheet stacked on the processing tray onto the stacktray, the overlapped area between the sheet stack and the buffer sheetsis reduced by an amount corresponding to the distance through which thesheet stack is conveyed by the predetermined amount, with the resultthat the sheet stack is separated from the buffer sheets positively, sothat the sheet stack can be discharged and stacked onto the stack traypositively. Further, since the sheets are conveyed by the rocking rollerpair and the trailing end assist, the sheets can be discharged quicklywithout generating dispersion in the sheet discharging time, therebyproviding an apparatus having a shorter processing time.

[0182] In the sheet processing apparatus, the receiving roller pair as arotary member pair can be engaged and disengaged with respect to eachother, jammed sheet can easily be removed.

What is claimed is:
 1. A sheet processing apparatus comprising: a sheet holding device capable of storing supplied sheets; a first sheet stacking tray on which sheets are stacked at a downstream side of said sheet holding device in a sheet conveying direction and on which the sheets are subjected to processing; a sheet discharging device for discharging the sheets stacked on said first sheet stacking tray; a second sheet stacking tray on which the sheets discharged by said sheet discharging device are stacked; and a controller for controlling said sheet discharging device and said sheet holding device when a succeeding sheet is not supplied to said sheet holding device for a predetermined time, in such a manner that, after the sheets on said first sheet stacking tray are discharged onto said second sheet stacking tray, the sheets stored in said sheet holding device are discharged onto said first sheet stacking tray.
 2. A sheet processing.apparatus comprising: a sheet holding device capable of storing supplied sheets; a first sheet stacking tray on which sheets stored by said sheet holding device or sheets passed without stopping at said sheet holding device are stacked and on which the sheets are subjected to processing; a second sheet stacking tray on which the sheets discharged from said first sheet stacking tray are stacked; a sheet conveying device for conveying the sheets stored in said sheet holding device and the sheets stacked on said first sheet stacking tray together and for stacking the sheets stored in said sheet holding device onto said first sheet stacking tray after the sheet stacked on said first sheet stacking tray are discharged onto said second sheet stacking tray; and a controller for controlling said sheet conveying device when a succeeding sheet is not supplied to said sheet holding device for a predetermined time, in such a manner that the sheets stacked on said first sheet stacking tray are discharged onto said second sheet stacking tray and the sheets stored in said sheet holding device are stacked onto said first sheet stacking tray.
 3. A sheet processing apparatus comprising: a sheet holding device capable of storing supplied sheets; a first sheet stacking tray on which sheets stored by said sheet holding-device or sheets passed without stopping at said sheet holding device are stacked and on which the sheets are subjected to processing; a first sheet conveying device capable of conveying the sheets stacked on said first sheet stacking tray by a predetermined amount at a downstream side of the sheets stored in said sheet holding device; a second sheet stacking tray on which the sheets discharged from said first sheet stacking tray are stacked; a second sheet conveying device for conveying the sheets stacked on said first sheet stacking tray and the sheets stored in said sheet holding device together after the sheets stacked on said first sheet stacking tray are conveyed by said first sheet conveying device by the predetermined amount at the downstream side and for discharging the sheets stacked on said first sheet stacking tray onto said second sheet stacking tray and for stacking the sheets stored in said sheet holding device onto said first sheet stacking tray; and a controller for controlling said sheet holding device and said second sheet conveying device when a succeeding sheet is not supplied to said sheet holding device for a predetermined time, in such a manner that the sheets stacked on said first sheet stacking tray are discharged onto said second sheet stacking tray and the sheets stored in said sheet holding device are stacked onto said first sheet stacking tray.
 4. A sheet processing apparatus comprising: a sheet holding device capable of storing supplied sheets; a first sheet stacking tray on which sheets are stacked at a downstream side of said sheet holding device in a sheet conveying direction and on which the sheets are subjected to processing; a sheet discharging device for discharging the sheets stacked on said first sheet stacking tray; a second sheet stacking tray on which the sheets discharged by said sheet discharging device are stacked; and a controller for controlling said sheet discharging device and said sheet holding device if sheet jam occurs at an upstream side of said sheet holding device, in such a manner that, after the sheets on said first sheet stacking tray are discharged onto said second sheet stacking tray, the sheets stored in said sheet holding device are discharged onto said first sheet stacking tray.
 5. A sheet processing apparatus comprising: a sheet holding device capable of storing supplied sheets; a first sheet stacking tray on which sheets stored by said sheet holding device or sheets passed without stopping at said sheet holding device are stacked and on which the sheets are subjected to processing; a second sheet stacking tray on which the sheets discharged from said first sheet stacking tray are stacked; a sheet conveying device for conveying the sheets stored in said sheet holding device and the sheets stacked on said first sheet stacking tray together and for stacking the sheets stored in said sheet holding device onto said first sheet stacking tray after the sheet stacked on said first sheet stacking tray are discharged onto said second sheet stacking tray; and a controller for controlling said sheet conveying device if sheet jam occurs at an upstream side of said sheet holding device, in such a manner that the sheets stacked on said first sheet stacking tray are discharged onto said second sheet stacking tray and the sheets stored in said sheet holding device are stacked onto said first sheet stacking tray.
 6. A sheet processing apparatus comprising: a sheet holding device capable of storing supplied sheets; a first sheet stacking tray on which sheets stored by said sheet holding device or sheets passed without stopping at said sheet holding device are stacked and on which the sheets are subjected to processing; a first sheet conveying device capable of conveying the sheets stacked on said first sheet stacking tray by a predetermined amount at a downstream side of the sheets stored in said sheet holding device; a second sheet stacking tray on which the sheets discharged from said first sheet stacking tray are stacked; a second sheet conveying device for conveying the sheets stacked on said first sheet stacking tray and the sheets stored in said sheet holding device together after the sheets stacked on said first sheet stacking tray are conveyed by said first sheet conveying device by the predetermined amount at the downstream side and for discharging the sheets stacked on said first sheet stacking tray onto said second sheet stacking tray and for stacking the sheets stored in said sheet holding device onto said first sheet stacking tray; and a controller for controlling said sheet holding device and said second sheet conveying device if sheet jam occurs at an upstream side of said sheet holding device, in such a manner that the sheets stacked on said first sheet stacking tray are discharged onto said second sheet stacking tray and the sheets stored in said sheet holding device are stacked onto said first sheet stacking tray. 